The present invention relates to a warning device to be suitably incorporated into cameras for giving warning statements in synthesized human voice or speech.
Recently, various kinds of automatic cameras have been provided for the purpose of the simple and easy operation of the camera without operational failures. In some of the latest automatic cameras, the operations of exposure and focus adjustments which are the most difficult camera operations are made automatically, enabling any photographer to take pictures only by operating a shutter release member. As to camera operations which are difficult to be made automatically or which render a camera costly due to the requirement of complicated mechanism and operation, it is desirable to make them manually. As the aforementioned operation, there may be exemplified a film loading operation, a preparatory operation for firing a strobe under conditions of subject brightness lower than that for the maximum exposure interval allowable for an exposure without incurring any adverse blurring effect from the normally expected hand motion of the photographer for a selected film speed and exposure aperture size, a changing operation of batteries or the like. When these operations are not carried out accurately and positively, photography results in a failure. For this reason, it is desirable to incorporate a warning device in a camera for giving the photographer warnings or calling attention that the camera condition or conditions should be corrected.
Generally, conventional warning devices incorporated in cameras give warnings or call attention by means of an illumination-producing device such as an LED arrangement or by means of a sound-producing device such as a speaker. These warning indications cannot make the photographer understood what is the camera condition to be corrected or adjusted.
There has recently been proposed a warning device built in a camera which is adapted to give a photographer specific voiced warnings. In such a camera, it is well known to utilize a voice synthesis circuit taking the form of a LS1 (large scaled integrated circuit) device due to the advantage of reduced current consumption thereof. The voice synthesis circuit operates to store in its non-volatile memory the information data in the form of digital signals separated for the respective specific warning statements or narrations to be given. When addressing the leading address of the data corresponding to the statement or narration by which warning is given of an operational condition, the data are sequentially retrieved for conversion into sound signals by means of an interpolating circuit and a sound generating circuit. Then the sound signals are simulated with a reasonance characteristic of human vocal cords through a digital filter and subsequently converted into synthesized acoustic signals in the form of analogue signals by a D/A converter.
When providing such warning devices with synthesized human speech, one of the problems associated with the warning device is concerned with a malfunction characterized by failure of a speaker to be driven directly with acoustic signals from the acoustic signal generating circuit due to the feebleness thereof. For this reason, the amplification of the acoustic signals by an amplifier is essential for driving the speaker for satisfactorily imparting warning statements in synthesized human speech. On the other hand, there occurs a different problem in that continuous current supply to the amplifier is wasteful and hence causes the accelerated discharge of a battery. A solution to the aforementioned problem is to supply current to the amplifier only when required (that is, only when the acoustic signals are generated). Such a solution, however due to the fact that the amplifier includes a lot of capacitors with a large capacity which require a relatively long time to be charged up, may incur a delay in the starting operation thereof attributed to the charge-up time, resulting in that a warning statement in synthesized human speech given by a speaker is inaudible at the beginning.